Hi i got a 96 318TI that i just got and dont know much about. When i am on the highway in 5th gear my RPM's are at 4,000 at 80 MPH. This seems high to me but im not sure any help would be nice. Thanks!

Thats just the way its geared, perfectly normal. You have a 3.45 geared differential because you have a manual. Also, 5th gear is 1:1, no overdrive.